The Meaning of Human Existence Read Online Free PDF Page A

images were amazing even to generations who regarded flybys and soft landings on other planets in the Solar System as routine. They are also immensely important, the equivalent of a seaman’s first glimpse of a new continent’s coastline, and a shout of, Land! Land!, where none might have existed. An estimated hundred billion star systems make up the Milky Way galaxy, and astronomers believe that all are orbited by an average of at least one planet. A small but still substantial fraction are likely to harbor life-forms—even if the organisms are only microbes living under extremely hostile conditions.
    The exoplanets (planets in other star systems) of the galaxy form a continuum. Astronomers have newly observed or at least inferred a bestiary of exoplanets more varied than anything previously imagined. There exist giant gas planets resembling Jupiter and Saturn, some hugely larger in volume. There are smaller rocky planets like our own, tiny specks orbiting at the right distance from the mother star to support life, fundamentally different from rocky planets at other distances (as Mercury and Venus are fatally near to the Sun and planetlike Pluto fatally far away). There exist planets that do not rotate, others that travel close to the mother star and then far away and back again in elliptical orbits.There probably exist orphaned rogue planets, thrown loose from the gravitational pull of their mother stars, drifting through outer space. Some of the exoplanets also have an entourage of one or more moons. In addition to great and continuous variation in size, location, and orbit, there are comparable gradients in the chemical composition of the body and atmosphere of the planets and their moons, derived from the particularities of their origin.
    Astronomers, being normal humans as well as scientists, are as awed as the rest of us by their discoveries. The discoveries affirm that Earth is not the center of the Universe—we’ve known that since Copernicus and Galileo—but just how far from the center has been hard to imagine. The tiny blue speck we call home is proportionately no more than that, a mote of stardust near the edge of our galaxy among a hundred billion or more galaxies in the universe. It occupies just one position in a continuum of planets, moons, and other planetlike heavenly bodies that we have just begun to understand. It would be becoming of us to speak modestly of our status in the cosmos. Let me offer a metaphor: Earth relates to the Universe as the second segment of the left antenna of an aphid sitting on a flower petal in a garden in Teaneck, New Jersey, for a few hours this afternoon.
    With botany and entomology thus fleetingly broughtto mind, it is appropriate to introduce another continuum, the diversity of life in Earth’s biosphere. At the time of this writing (in 2013) there are 273,000 known species of plants in the living flora of Earth, a number expected to rise to 300,000 as more expeditions take to the field. The number of all known species of organisms on Earth, plants, animals, fungi, and microbes, is about 2 million. The actual number, combining known and unknown, is estimated to be at least three times that number, or more. The roster of newly described species is about 20,000 a year. The rate will certainly grow, as a multitude of still poorly explored tropical forest fragments, coral reefs, seamounts, and uncharted ridges and canyons of the deep ocean floor become better known. The number of described species will accelerate even faster with exploration of the largely unknown microbial world, now that the technology needed for the study of extremely small organisms has become routine. There will come to light strange new bacteria, archaeans, viruses, and picozoans that still swarm unseen everywhere on the surface of the planet.
    As the census of species proceeds, other continua of biodiversity are being mapped. They include the unique biology of each living species and the long,